Spectroscopic measurement techniques for measuring light emission efficiency and the like of a measurement object with an integrator and a spectroscopic detector have been known. The integrator includes an internal space in which the measurement object is disposed, a light input portion for inputting the light output from a light source into the internal space, and a light output portion for outputting the measurement target light from the internal space to the outside. The internal space of the integrator is, for example, spherical, and covered with an inner wall surface having high reflectance and excellent diffuseness. Alternatively, the internal space of the integrator is, for example, hemispherical, and in this case, an inner wall of a hemispherical portion has a wall surface with high reflectance and excellent diffuseness and a planar portion is a flat mirror with high reflectance.
In the integrator, excitation light output from the light source can be input from the light input portion into the internal space, and the excitation light can be diffused and reflected multiple times in the internal space. In addition, in the integrator, emission light (such as fluorescence), generated when the measurement object disposed in the internal space is irradiated with the excitation light, can also be diffused and reflected multiple times in the internal space. Then, the integrator outputs the measurement target light from the internal space to the outside through the light output portion. The measurement target light is the excitation light and/or the emission light.
The spectroscopic detector disperses the measurement target light output from the integrator to the outside, and acquires spectrum data. The spectroscopic detector disperses the measurement target light into respective wavelength components through a spectroscopic element such as a grating or a prism, and detects the intensity of the dispersed light of each wavelength using an optical sensor. The optical sensor has a plurality of light receiving portions arrayed one-dimensionally, and by detecting the light intensity of the wavelength component by the light receiving portion corresponding to each wavelength, the spectrum data of the measurement target light can be acquired. Then, by analyzing the spectrum data, the luminous efficiency and the like of the measurement object can be measured without depending on the angle characteristic and the like of the light emission of the measurement object.
In the spectroscopic measurement technique using the integrator, the measurement object may be the organic EL (electroluminescence) material or the fluorescent material. The measurement object may be in the arbitrary form, such as a solution, a thin film, or powder. For such a measurement object, evaluation of the photoluminescence quantum yield (internal quantum efficiency) is important. The photoluminescence quantum yield refers to the ratio of the number of photons of the emission light generated in the measurement object to the number of photons of the excitation light absorbed by the measurement object. The spectroscopic measurement technique using the integrator is preferably applicable for evaluating the photoluminescence quantum yield of the measurement object.
The up-conversion luminescence material has been researched using such a spectroscopic measurement technique (see Non Patent Document 1). In the up-conversion luminescence phenomenon, the light (up-conversion light) having a shorter wavelength than the excitation light is generated. The up-conversion occurs in the non-linear optical phenomenon such as the multiphoton absorption and the second-order or third-order harmonic generation, the multistage excitation phenomenon of the rare-earth element, the phenomenon based on the triplet-triplet annihilation (TTA), or the like.
In the spectroscopic measurement technique described in Non Patent Document 1, the luminous efficiency of the up-conversion luminescence material which is the measurement object is measured by disposing a filter, having a transmission characteristic that is different in excitation light measurement and up-conversion light measurement, on an optical path between the integrator and the spectroscopic detector.